Method for calculating power capability of battery packs using advanced cell model predictive techniques

• US 20050110498A1
• Filed: 03/25/2004
• Published: 05/26/2005
• Est. Priority Date: 11/20/2003
• Status: Active Grant

• Current Assignee: LG Energy Solution Limited (LG Corporation)
• Original Assignee: LG Chem Limited (LG Corporation)
• Inventors: Plett, Gregory L.
• Granted Patent: US 7,321,220 B2
• Time in Patent Office: Days
• US Class Current: 324/433
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: G01R 31/3828 using current integration

Abstract

The present invention relates to a method and an apparatus for estimating discharge and charge power of battery applications, including battery packs used in Hybrid Electric Vehicles (HEV) and Electric Vehicles (EV). One charge/discharge power estimating method incorporates voltage, state-of-charge (SOC), power, and current design constraints and works for a user-specified prediction time horizon Δt. At least two cell models are used in calculating maximum charge/discharge power based on voltage limits. The first is a simple cell model that uses a Taylor-series expansion to linearize the equation involved. The second is a more complex and accurate model that models cell dynamics in discrete-time state-space form. The cell model can incorporate a inputs such as temperature, resistance, capacity, etc. One advantage of using model-based approach is that the same model may be used in both Kalman-filtering to produce the SOC and the estimation of maximum charge/discharge current based on voltage limits.

Claims

1. A method for estimating the maximum discharge power of a battery comprising:

calculating a maximum discharge current of said battery based on voltage limits of said battery;

calculating said maximum discharge power based on said maximum discharge current value.

2. The method of claim 1 further comprising:

calculating a maximum discharge current of said battery based on state-of-charge limits of said battery;

calculating a maximum discharge current of said battery based on current limits of said battery,

wherein said maximum discharge power is calculated from a minimum value of discharge current chosen among said calculated maximum discharge current based on voltage limits, said calculated maximum discharge current based on state-of-charge limits, and said calculated maximum discharge current based on current limits.

3. The method of claim 2 wherein said estimating of maximum discharge power takes into account a user-defined horizon of Δ

t.

4. The method of claim 2 wherein said step of calculating maximum discharge current of said battery based on state-of-charge limits obtains a state-of-charge by using a Kalman filtering method.

5. The method of claim 4 wherein an estimate of the uncertainty value yielded by said Kalman filtering method is used to find a confidence level of said calculated maximum discharge current.

6. The method of claim 2 wherein said battery is a battery pack comprising n cells.

7. The method of claim 6 wherein said step of calculating maximum discharge current of said battery based on state-of-charge limits calculates the current limits of each cell k in said battery pack using the equation

8. The method of claim 7 wherein maximum discharge current of said battery pack based on state-of-charge limits is

9. The method of claim 1 wherein said step of calculating maximum discharge current of said battery based on voltage limits uses a cell model.

10. The method of claim 9 wherein cell model is solved by a Taylor-series expansion.

11. The method of claim 9 wherein said cell model is solved by using a discrete time-state space model.

12. The method of claim 9 wherein said battery is a battery pack comprising n cells.

13. The method of claim 12 wherein said cell model is

v_k(t+Δ

t)OCV(z_k(t+Δ

t))−

R×

i_k(t)

wherein v_k(t+Δ

t) denotes the cell voltage for cell k for the time period t units into the future, OCV(z_k(t+Δ

t)) denotes the open cell voltage as a function of the state of charge z_k for cell k for the time period t units into the future, R is a constant that denotes the cell'"'"'s internal resistance, and i_k(t) denotes the cell current.

14. The method of claim 13 wherein said maximum discharge current based on voltage limits is obtained by solving, through Taylor-series expansion

15. The method of claim 14 wherein said

16. The method of claim 13 wherein said cell model is solved by using a discrete time-state space model.

17. The method of claim 16 wherein said discrete time-state space model is

x_k[m+1]=ƒ

(x_k[m], u_k[m])
v_k[m]=g(x_k[m],u_k[m])

wherein m denotes the discrete time sample index, x_k[m] denotes the vector function of time and the state of the system, u_k[m] denotes the input to the system and includes cell current i_k[m] as a component, and ƒ

(•

) and g(•

) are functions chosen to model the cell dynamics.

18. The method of claim 17 wherein said u_k[m] inputs includes temperature.

19. The method of claim 17 wherein said u_k[m] inputs includes resistance.

20. The method of claim 17 wherein said u_k[m] inputs includes capacity.

21. The method of claim 17 wherein

22. The method of claim 21 wherein said equality is found by a using bisection search algorithm.

23. The method of claim 17 wherein the equation x_k[m+T]=Ax_k[m]+Bu_k[m] is linear, wherein A and B are constant matrices.

24. The method of claim 12 wherein said minimum value of discharge current is chosen by using the equation

25. The method of claim 24 wherein said maximum discharge power is calculated by solving

26. The method of claim 25 wherein

27. The method of claim 2 wherein any said state-of-charge limits, voltage limits, and current limits can be eliminated from said calculations by using positive infinity or negative infinity to represent said eliminated limits in said calculations.

28. The method of claim 2 wherein any said state-of-charge limits, voltage limits, and current limits is dependent on temperature.

29. The method of claim 2 wherein said calculated maximum discharge power is checked to ensure that it falls within power limits of said battery.

30. A method for estimating the minimum charge power of a battery comprising:

calculating a minimum charge current of said battery based on voltage limits of said battery;

calculating said minimum charge power based on said maximum discharge current value.

31. The method of claim 30 further comprising:

calculating a minimum charge current of said battery based on state-of-charge limits of said battery;

calculating a minimum charge current of said battery based on current limits of said battery,

wherein said minimum charge power is calculated from a maximum value of charge current chosen among said calculated minimum charge current based on voltage limits, said calculated minimum charge current based on state-of-charge limits, and said calculated minimum charge current based on current limits.

32. The method of claim 31 wherein said estimating of minimum charge power takes into account a user-defined horizon of Δ

t.

33. The method of claim 31 wherein said step of calculating minimum charge current of said battery based on state-of-charge limits obtains a state-of-charge by using a Kalman filtering method.

34. The method of claim 33 wherein an estimate of the uncertainty value yielded by said Kalman filtering method is used to find a confidence level of said calculated minimum charge current.

35. The method of claim 31 wherein said battery is a battery pack comprising n cells.

36. The method of claim 35 wherein said step of calculating minimum charge current of said battery based on state-of-charge limits calculates the current limits of each cell k in said battery pack using the equation

37. The method of claim 36 wherein minimum charge current of said battery pack based on state-of-charge limits is

38. The method of claim 30 wherein said step of calculating minimum charge current of said battery based on voltage limits uses a cell model.

39. The method of claim 38 wherein cell model is solved by a Taylor-series expansion.

40. The method of claim 38 wherein said cell model is solved by using a discrete time-state space model.

41. The method of claim 38 wherein said battery is a battery pack comprising n cells.

42. The method of claim 41 wherein said cell model is

v_k(t+Δ

t)=OCV(z_k(t+Δ

t))−

R×

i_k(t)

wherein v_k(t+Δ

t) denotes the cell voltage for cell k for the time period t units into the future, OCV(z_k(t+Δ

t)) denotes the open cell voltage as a function of the state of charge z_k for cell k for the time period t units into the future, R is a constant that denotes the cell'"'"'s internal resistance, and i_k(t) denotes the cell current.

43. The method of claim 42 wherein said minimum charge current based on voltage limits is obtained by solving, through Taylor-series expansion

44. The method of claim 43 wherein said

45. The method of claim 42 wherein said cell model is solved by using a discrete time-state space model.

46. The method of claim 45 wherein said discrete time-state space model is

x_k[m+1]=ƒ

(x_k[m], u_k[m])
v_k[m]=g(x_k[m],u_k[m])

wherein m denotes the discrete time sample index, x_k[m] denotes the vector function of time and the state of the system, u_k[m] denotes the input to the system and includes cell current i_k[m] as a component, and ƒ

(•

) and g(•

) are functions chosen to model the cell dynamics.

47. The method of claim 46 wherein said u_k[m] inputs includes temperature.

48. The method of claim 46 wherein said u_k[m] inputs includes resistance.

49. The method of claim 46 wherein said u_k[m] inputs includes capacity.

50. The method of claim 46 wherein

51. The method of claim 50 wherein said equality is found by a using bisection search algorithm.

52. The method of claim 46 wherein the equation x_k[m+T]=Ax_k[m]+Bu_k[m] is linear, wherein A and B are constant matrices.

53. The method of claim 41 wherein said maximum value of charge current is chosen by using the equation

54. The method of claim 53 wherein said minimum charge power is calculated by solving

55. The method of claim 54 wherein

56. The method of claim 31 wherein any said state-of-charge limits, voltage limits, and current limits can be eliminated from said calculations by using positive infinity or negative infinity to represent said eliminated limits in said calculations.

57. The method of claim 31 wherein any said state-of-charge limits, voltage limits, and current limits is dependent on temperature.

58. The method of claim 31 wherein said calculated minimum charge power is checked to ensure that it falls within power limits of said battery.

59. A power estimating apparatus for estimating maximum discharge power of a battery comprising:

a voltage measurement means for measuring the voltage of said battery;

a temperature measurement means for measuring the temperature of said battery;

a current measurement means for measuring the current of said battery;

an estimator means for calculating maximum discharge power of said battery, wherein said estimator means uses measurements from said voltage measurement means, said temperature measurement means, and current measurement means and performs calculations to estimate maximum discharge power of said battery, said estimator means comprising;

means for calculating a maximum discharge current of said battery based on voltage limits of said battery;

means for calculating a maximum discharge current of said battery based on state-of-charge limits of said battery;

means for calculating a maximum discharge current of said battery based on current limits of said battery, wherein said maximum discharge power is calculated from a minimum value of discharge current chosen among said calculated maximum discharge current based on voltage limits, said calculated maximum discharge current based on state-of-charge limits, and said calculated maximum discharge current based on current limits.

60. The power estimating apparatus of claim 59 wherein said estimator means takes into account a user-defined horizon of Δ

t.

61. The power estimating apparatus of claim 59 wherein said means for calculating maximum discharge current of said battery based on state-of-charge limits obtains a state-of-charge by using a Kalman filtering method.

62. The power estimating apparatus of claim 61 wherein an estimate of the uncertainty value yielded by said Kalman filtering method is used to find a confidence level of said calculated maximum discharge current.

63. The power estimating apparatus of claim 61 wherein said battery is a battery pack comprising n cells.

64. The power estimating apparatus of claim 61 wherein said means for calculating maximum discharge current of said battery based on voltage limits uses a cell model.

65. The power estimating apparatus of claim 61 wherein cell model is solved by a Taylor-series expansion.

66. The power estimating apparatus of claim 61 wherein said cell model is solved by using a discrete time-state space model.

67. An power estimating apparatus for estimating minimum charge power of a battery comprising:

a voltage measurement means for measuring the voltage of said battery;

a temperature measurement means for measuring the temperature of said battery;

a current measurement means for measuring the current of said battery;

an estimator means for calculating minimum charge power of said battery, wherein said estimator means uses measurements from said voltage measurement means, said temperature measurement means, and current measurement means and performs calculations to estimate minimum charge power of said battery, said estimator means comprising;

means for calculating a minimum charge current of said battery based on voltage limits of said battery;

means for calculating a minimum charge current of said battery based on state-of-charge limits of said battery;

means for calculating a minimum charge current of said battery based on current limits of said battery, wherein said minimum charge current power is calculated from a maximum value of discharge current chosen among said calculated minimum charge current based on voltage limits, said calculated minimum charge current based on state-of-charge limits, and said calculated minimum charge current based on current limits.

68. The power estimating apparatus of claim 67 wherein said estimator means takes into account a user-defined horizon of Δ

t.

69. The power estimating apparatus of claim 67 wherein said means for calculating minimum charge current of said battery based on state-of-charge limits obtains a state-of-charge by using a Kalman filtering method.

70. The power estimating apparatus of claim 69 wherein an estimate of the uncertainty value yielded by said Kalman filtering method is used to find a confidence level of said calculated maximum discharge current.

71. The power estimating apparatus of claim 69 wherein said battery is a battery pack comprising n cells.

72. The power estimating apparatus of claim 69 wherein said means for calculating minimum current of said battery based on voltage limits uses a cell model.

73. The power estimating apparatus of claim 69 wherein cell model is solved by a Taylor-series expansion.

74. The power estimating apparatus of claim 69 wherein said cell model is solved by using a discrete time-state space model.